1. Field of the Invention
The present invention relates to a solid-state image sensor and a camera.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2012-191400 discloses an image sensor which includes pixels each having a pair of photodiodes and detects a focus by a pupil division method. The image sensor has a first readout mode and a second readout mode. In the first readout mode, the image sensor reads out added output signals from the pairs of photodiodes of all the pixels to record the image generated by imaging. In the second readout mode, the image sensor reads out added output signals from the pairs of photodiodes of all the pixels to display an image on a liquid crystal display device and also reads out an output signal (single output signal) from one of the photodiodes of each pixel to detect a focus. Note that Japanese Patent Laid-Open No. 2012-191400 gives no consideration to the readout of signals from light-shielded pixels for the detection of dark currents in the pixels.
In general, a solid-state image sensor has a light-shielded pixel area (optical black pixel area) in which light-shielded pixels (optical black pixels) for obtaining reference signals are arranged. The light-shielded pixel area is arranged adjacent to a light-receiving pixel area in which light-receiving pixels (effective pixels) for detecting the optical image formed on an image sensing surface are arranged. That is, the pixel array of the solid-state image sensor includes the light-receiving pixel area and the light-shielded pixel area. A one-frame signal output from the solid-state image sensor includes a signal in the light-shielded pixel area and a signal in the light-receiving pixel area.
When the solid-state image sensor designed to detect a focus by the pupil division method outputs a signal from one of a pair of photoelectric converters constituting each light-receiving pixel, outputting also a signal from one of a pair of photoelectric converts constituting each light-shielded pixel takes a long period of time to output all signals.